8 3/4 Carrier

[roadrunnerh]

I need some input. I understand how the three carriers compair as far as pinion gear sizes, 741 - 489 - 742 (489 being the largest at 1 7/8 but tappered, and 742 diameter being 1 3/4 but not tappered, and the 741 being the smallest - but very underrated).

How can you tell the condition of a used unit other than a visual inspection for cracked / broken teeth?

What are the differences in sure grip units?

I want to avoid buying a used unit that was pounded hard.

Would I be better off buying a used one-legger and buying a new sure grip unit for it?

Does anyone here have a carrier they wanna sell?

 

[A31PKG]

From street-only experience, I can attest to the fact that the 8 3/4 rear is a pretty durable unit. I dare say this is true for any of the above-mentioned casting numbers, although if given a choice I would probably stay away from the 1 3/8" dia. 741 unit. The 1 7/8" tapered pinion 489 unit is often deemed the strongest, but I have to wonder if the 742 unit may be a better choice since its pinion is 1 3/4" in dia for its entire length? That said, I've had both casting numbers in various cars over the years and neither have given me a bit of trouble. As far as sure-grip differences, 68 & back units use clutches, and 69 & up use cones. Supposedly the cone style is more durable? I also remember most guys at the track running the 8 3/4" because it's much easier to swap gears between runs. Look for blueing of the carrier caps, races and bearings, & gears themselves. Also look for metal flakes especially on the bearing rollers - if you can see in there.... I'm sure someone else can offer additional info.

 

[69hemibeep]

The early clutch type unit is rebuild able with a new clutch pack and the cone type can be reconditioned with some machine work. I have a copy of a tech sheet on how to do it.

 

[ACME A12]

Not much to add, Harry. They pretty well covered it.

I've pretty much beaten the snot out of both 742s and 489s...with equal fervor...hard to beat them or break them, especially if you're on street tires.

FWIW - I run a 741 in the little gold '74 Duster. No issues there either, but it's a very mild 340, not much convertor or gear (maybe 2,500 behind that engine and 3.55's), and of course the veritable "spin me all you want" Radial T/A's. I assume that you're asking about this for your new little A-Bomb project...which is why I mention this. You could get away with the 741 on the street, unless you're going straight axle gasser with this thing like Bob is with his...

 

[moparchris]

I have seen 10 second big block street cars with 741 cases in them. I would stay away from the cone sure grip too many of them need expensive machine work (unless you own a lathe or mill) to get them to work correctly. The clutch types are more durable and have better holding power. For used units you will want to check back lash since a bearing issue will show up there and twist it with your hand by the yoke. It should be smooth and fairly easy to turn. Visually inspect the teeth and if you know how, run a pattern on the gear teeth to see if it has been set up right.

 

[A31PKG]

I have seen 10 second big block street cars with 741 cases in them. I would stay away from the cone sure grip too many of them need expensive machine work (unless you own a lathe or mill) to get them to work correctly. The clutch types are more durable and have better holding power....

There are 10 second cars without rollbars too.... I would still avoid a 741 case. To each his own. The cone style diff must have been an improvement or Ma MOPAR would not have switched. Or maybe it was a cost thing? I'm no expert on the clutch vs. cone debate, but in street trim at least, I have never had an issue with either style. The biggest problem we ever had with any 8 3/4 diff were leaking pinion seals. Otherwise they were pretty bulletproof.

 

[V269]

All I had access to years ago when I was putting the pot and gears in my car was a 741 case. It's been in there over 20 years and I have beat on it good. No problems and it is still in the car. 3.91 gears too. I'll leave it there until it explodes I guess. :yesnod:

 

[A31PKG]

Sorry about my previous post, I neglected to hit the "decaf" button this morning!

:grouphug:

 

[V269]

 

[ACME A12]

Sorry about my previous post, I neglected to hit the "decaf" button this morning!

:grouphug:

Craig, I think you're pretty safe no matter what in this crowd...

 

[A31PKG]

WHEW! That's a relief! :yesnod: